TWI836146B - Multi-imaging mode image alignment - Google Patents

Abstract

Methods and systems for aligning images of a specimen generated with different modes of an imaging subsystem are provided. One method includes separately aligning first and second images generated with first and second modes, respectively, to a design for the specimen. For a location of interest in the first image, the method includes generating a first difference image for the location of interest and the first mode and generating a second difference image for the location of interest and the second mode. The method also includes aligning the first and second difference images to each other and determining information for the location of interest from results of the aligning.

Description

Multi-imaging mode image alignment

The present invention generally relates to methods and systems for aligning images of a sample produced using different modes of an imaging subsystem.

The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section.

Inspection procedures are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yields in the process and therefore higher profits. Inspection has always been an important part of manufacturing semiconductor devices. However, as the size of semiconductor devices decreases, inspection becomes even more important for successful manufacturing of acceptable semiconductor devices because smaller defects can lead to device failure.

Many inspection tools have adjustable parameters for many of the output (e.g., image) generating components of the tools. The parameters of one or more components (such as energy source(s), polarizer(s), lens(s), detector(s), and the like) may be altered depending on the type of sample being inspected and the characteristics of the defect (DOI) of interest on the sample. For example, different types of samples may have significantly different characteristics, which may cause the same tool with the same parameters to image the sample in significantly different ways. Additionally, because different types of DOIs may have significantly different characteristics, inspection system parameters that are suitable for detecting one type of DOI may not be suitable for detecting another type of DOI. Furthermore, different types of samples may have different noise sources, which may interfere with the detection of DOIs on the sample in different ways.

The development of inspection tools with adjustable parameters has also led to an increase in the use of inspection procedures that involve scanning a sample with more than one combination of parameter values (otherwise referred to as "modes") such that different modes can be used to detect different defect types. . For example, one mode may have greater sensitivity for detecting one type of defects, while another mode may have greater sensitivity for detecting another type of defects. Therefore, using both modes, one inspection system may be able to detect both types of defects with acceptable sensitivity.

Several currently used methods can be used for optical mode selection (OMS) to find the best detection mode. When a detection process uses only one mode of the detection tool, mode selection can be relatively simple. For example, a performance metric (such as DOI capture versus nuisance rejection) can be compared for each mode to identify the mode with the best performance. However, when more than one mode is used for detection, this process becomes exponentially more complex and difficult. For example, one can simply compare the performance metrics of different modes and then select the first two or more modes for detection, but this will not necessarily result in a better detection process than if only the first mode was used.

Instead, the impetus for using more than one mode for detection is often that detection is relatively difficult to initiate, for example, DOIs are relatively difficult to separate from noise and/or clutter points are relatively difficult to suppress. For such detection, ideally, two or more modalities will complement each other in some way, such that, for example, results produced by one modality enhance those produced by another modality. In one such instance, even if the results produced by one model are not particularly "good" per se, in the right context they can be used to separate DOIs and clutter points from other results produced by another model, thereby Enhance the results produced by another mode.

Often, it is difficult to identify such complementary modes for several reasons. One such reason may be that the number of variable settings on a test tool is quite large, resulting in a large number of modes and an even larger number of mode combinations that can be evaluated. Some test mode selection procedures are designed to simplify this process by eliminating some modes or mode combinations before the evaluation begins. Even so, the number of modes and mode combinations may be too large to evaluate them all.

Difficulties in selecting and using multiple modes for inspection or other image-based processes such as defect inspection and metrology may also arise from difficulties in aligning images from multiple modes with one another or otherwise identifying locations in images from different modes that correspond to the same location on a sample. For example, to the best of the inventor's knowledge, tile images from different modes of an optical detector have never before been aligned with one another. Inter-mode image alignment is also difficult (if not impossible) due to the differences in images from different modes. In other words, the differences between images from multiple modes that make them useful for applications such as inspection, defect inspection, and the like also make it difficult to align the images with one another so that they can be used in a complementary manner.

Accordingly, it would be advantageous to develop systems and methods for aligning images of a sample produced using different modes of an imaging subsystem that do not suffer from one or more of the disadvantages described above.

The following description of the various embodiments should in no way be interpreted as limiting the scope of the accompanying invention claims.

One embodiment relates to a system configured for aligning images of a sample produced using different modes of an imaging subsystem. The system includes an imaging subsystem configured to generate first and second images of a sample using first and second modes of the imaging subsystem, respectively. The system also includes one or more computer systems configured to separately align the first image and the second image to a design of the sample. For a location of interest in the first image, the one or more computer systems are also configured to subtract one of the locations of interest from a test image portion of the first image of the location of interest The first reference image generates a first difference image of the location of interest. The one or more computer systems are further configured to generate one of the locations of interest by subtracting a second reference image of the location of interest from a test image portion of the second image of the location of interest Second difference image. Additionally, the one or more computer systems are configured to align the first difference image and the second difference image with each other and determine the result from aligning the first difference image and the second difference image with each other. Information about the location of interest. The system can be further configured as described herein.

Another embodiment relates to a method for aligning images of a sample generated using different modes of an imaging subsystem. The method includes generating a first image and a second image of a sample using a first mode and a second mode of an imaging subsystem, respectively. The method also includes the separate alignment, generating a first difference image, generating a second difference image, alignment, and determining information steps described above, which are performed by one or more computer systems. Each of the steps of the method described above may be further performed as further described herein. In addition, the embodiment of the method described above may include any other step (several) of any other method (several) described herein. In addition, the method described above may be performed by any of the systems described herein.

Another embodiment relates to a non-transitory computer-readable medium storing program instructions that can be executed on a computer system to perform a computer-implemented method for aligning images of a sample generated using different modes of an imaging subsystem. The computer-implemented method includes the steps of the method described above. The computer-readable medium can be further configured as described herein. The steps of the computer-implemented method can be performed as further described herein. In addition, the computer-implemented method on which the program instructions can be executed can include any other step(s) of any other method(s) described herein.

The term "Defect of Interest (DOI)" as used herein is defined as a defect that is detected on a sample and is in fact an actual defect on the sample. Therefore, the DOI is of interest to the user because the user is usually concerned with the actual number and type of defects detected on the sample. For some background, the term "DOI" is used to refer to a subset of all actual defects on a sample that includes only the actual defects of concern to a user. For example, there may be multiple types of actual defects present on any given sample, and one or more of them may be of greater concern to the user than one or more other types. However, in the context of the embodiments described herein, the term "DOI" is used to refer to any and all real defects on a sample.

As used herein, the terms "design" and "design data" generally refer to the physical design (layout) of an IC and the data derived from the physical design through complex simulations or simple geometry and Boolean operations. The physical design may be stored in a data structure such as a Graphic Data Stream (GDS) file, any other standard machine-readable file, any other suitable file known in the art, and a design database. A GDSII file is one of a class of files used for representation of design layout data. Other examples of such files include GL1 and OASIS files and proprietary file formats such as Reducible Reticle Design File (RDF) data, which is proprietary to KLA, Milpitas, California. Additionally, an image of a reticle captured by a reticle inspection system and/or derivatives thereof can be used as a "proxy" or "proxies" for a design. This reticle image or a derivative thereof can be used as a substitute for a design layout in any embodiment described herein that uses a design. The design can include any other design data or design data proxies described in commonly owned U.S. Patent No. 7,570,796, issued August 4, 2009 to Zafar et al. and commonly owned U.S. Patent No. 7,676,077, issued March 9, 2010 to Kulkarni et al., both of which are incorporated herein by reference as if fully set forth. Additionally, the design data may be standard cell library data, integrated layout data, design data for one or more layers, derivatives of the design data, and full or partial chip design data.

"Design" and "design data" as described herein also refer to information and data generated by a semiconductor device designer in a design process and thus can be used in the embodiments described herein well before the design is printed on any physical wafer. A "design" or "physical design" can also be a design as it would ideally be formed on a wafer. In this way, a design may not include features of the design that will not be printed on a wafer, such as optical proximity correction (OPC) features that are added to the design to enhance the printing of features on the wafer but are not actually printed themselves.

The terms “first” and “second” are used herein only to indicate two things that are different from each other and are not used to indicate any temporal, spatial, preferred or other characteristics of the elements referred to herein as “first” and “second”.

Referring now to the drawings, it should be noted that the drawings are not drawn to scale. In particular, the proportions of some elements of the drawings are greatly exaggerated to emphasize the characteristics of the elements. It should also be noted that the drawings are not drawn to the same scale. The same element symbols have been used to indicate elements that may be similarly configured and shown in more than one figure. Unless otherwise specified herein, any of the elements described and shown may include any suitable commercially available elements.

Generally speaking, embodiments described herein are configured for aligning images of a sample produced using different modes of an imaging subsystem. In particular, embodiments are configured to align images from multiple modalities with each other. Embodiments described herein are particularly advantageous for image alignment for multi-modal imaging applications such as optical inspection.

In some embodiments, the sample is a wafer. The wafer may include any wafer known in semiconductor technology. Although some embodiments may be described herein with respect to one or several wafers, embodiments are not limited to samples in which they may be used. For example, embodiments described herein may be used with samples such as reticle masks, flat panels, personal computer (PC) boards, and other semiconductor samples.

One embodiment relates to a system configured for aligning images of a sample produced using different modes of an imaging subsystem. One embodiment of such a system is shown in Figure 1 . The system includes an imaging subsystem 100 configured to generate first and second images of a sample using first and second modes of the imaging subsystem, respectively. The imaging subsystem is coupled to one or more computer systems 102 . In the embodiment shown in Figure 1, the imaging subsystem is configured as a light-based imaging subsystem. In this manner, in some embodiments, the imaging subsystem is configured to generate the first image and the second image using light. However, in other embodiments described herein, the imaging subsystem is configured as an electron beam or charged particle beam imaging subsystem. In this manner, in other embodiments, the imaging subsystem is configured to generate the first image and the second image using electrons.

Generally speaking, the imaging subsystem described herein includes at least an energy source, a detector, and a scanning subsystem. The energy source is configured to generate energy directed to a sample through the imaging subsystem. The detector is configured to detect energy from the sample and generate an output in response to the detected energy. The scanning subsystem is configured to change a location on the sample, direct energy to that location, and detect energy from that location.

In the light-based imaging subsystem described herein, energy directed to a sample includes light, and energy detected from a sample includes light. For example, in an embodiment of the system shown in FIG. 1 , the imaging subsystem includes an illumination subsystem configured to direct light to a sample 14. The illumination subsystem includes at least one light source. For example, as shown in FIG. 1 , the illumination subsystem includes a light source 16. In one embodiment, the illumination subsystem is configured to direct light to the sample at one or more incident angles that may include one or more oblique angles and/or one or more normal angles. For example, as shown in FIG. 1 , light from the light source 16 is directed at an oblique incident angle through the optical element 18 and then through the lens 20 to the sample 14. The oblique angle of incidence may include any suitable oblique angle of incidence that may vary depending on, for example, the characteristics of the sample and the procedures performed on the sample.

The illumination subsystem may be configured to direct light to the sample at different angles of incidence at different times. For example, the imaging subsystem may be configured to change one or more characteristics of one or more elements of the illumination subsystem so that light may be directed to the sample at an angle of incidence different from that shown in FIG. 1 . In one such example, the imaging subsystem may be configured to move the light source 16, optical element 18, and lens 20 so that light is directed to the sample at a different oblique angle of incidence or a normal (or near-normal) angle of incidence.

In some examples, the imaging subsystem can be configured to direct light to the sample at more than one angle of incidence at the same time. For example, the lighting subsystem may include more than one lighting channel, one of the lighting channels may include the light source 16, the optical element 18, and the lens 20 as shown in FIG. 1, and the other of the lighting channels (not shown in FIG. shown) may include similar elements that may be in different or identical configurations or may include at least one light source and possibly one or more other components (such as those further described herein). If this light is directed to the sample at the same time as other light, one or more properties (e.g., wavelength, polarization, etc.) of the light directed to the sample at different angles of incidence may differ, allowing detection at(s) The device distinguishes light from illuminating the sample at different angles of incidence.

In another example, the illumination subsystem may include only one light source (e.g., source 16 shown in FIG. 1 ) and light from the light source may be separated into different optical paths (e.g., based on wavelength, polarization, etc.) by one or more optical elements (not shown) of the illumination subsystem. Light in each of the different optical paths may then be directed to the sample. Multiple illumination channels may be configured to direct light to the sample at the same time or at different times (e.g., when different illumination channels are used to illuminate the sample sequentially). In another example, the same illumination channel may be configured to direct light with different characteristics to the sample at different times. For example, in some instances, optical element 18 can be configured as a spectral filter and the properties of the spectral filter can be changed in a variety of different ways (e.g., by swapping out one spectral filter with another spectral filter) so that light of different wavelengths can be directed to the sample at different times. The illumination subsystem can have any other suitable configuration known in the art for directing light of different or the same characteristics to the sample sequentially or simultaneously at different or the same incident angles.

The light source 16 may comprise a broadband plasma (BBP) light source. In this manner, the light generated by the light source and directed toward the sample may comprise broadband light. However, the light source may comprise any other suitable light source, such as a laser. The laser may comprise any suitable laser known in the art and may be configured to produce light of any suitable wavelength(s) known in the art. Additionally, the laser may be configured to produce monochromatic or near monochromatic light. In this manner, the laser may be a narrowband laser. The light source may also comprise a polychromatic light source that produces light of multiple discrete wavelengths or bands.

Light from optical element 18 may be focused onto sample 14 by lens 20. Although lens 20 is shown in FIG. 1 as a single refractive optical element, in practice, lens 20 may include a number of refractive and/or reflective optical elements that in combination focus light from the optical element onto the sample. The illumination subsystem shown in FIG. 1 and described herein may include any other suitable optical elements (not shown). Examples of such optical elements include, but are not limited to, polarizing components (several), spectral filters (several), spatial filters (several), reflective optical elements (several), apodizers (several), beam splitters (several), apertures (several), and the like which may include any such suitable optical elements known in the art. In addition, the system may be configured to change one or more of the elements of the illumination subsystem based on the type of illumination to be used for imaging.

The imaging subsystem may also include a scanning subsystem configured to change the position on the sample (to direct light to and detect light from the position) and possibly cause the light to scan across the sample. For example, the imaging subsystem may include a stage 22 on which sample 14 is positioned during imaging. The scanning subsystem can include any suitable mechanical and/or robotic assembly (including a stage) that can be configured to move the sample such that light can be directed to and detected from different locations on the sample. twenty two). Additionally or alternatively, the imaging subsystem may be configured such that one or more optical elements of the imaging subsystem perform some scan of light across the sample such that light can be directed to and detected from different locations on the sample. Metering. In instances where the light is scanned across the sample, the light may be scanned across the sample in any suitable manner, such as in a serpentine path or in a spiral path.

The imaging subsystem further includes one or more detection channels. At least one of the detection channel(s) includes a detector configured to detect light from the sample due to illumination of the sample by the system and generate an output in response to the detected light. For example, the imaging subsystem shown in Figure 1 includes two detection channels, one detection channel is formed by the light collector 24, the element 26 and the detector 28 and the other detection channel is formed by the light collector 30, the element 26 and the detector 28. 32 and detector 34 are formed. As shown in Figure 1, two detection channels are configured to collect and detect light at different collection angles. In some examples, two detection channels are configured to detect scattered light, and the detection channels are configured to detect light scattered from the sample at different angles. However, one or more of the detection channels may be configured to detect another type of light from the sample (eg, reflected light).

As further shown in FIG. 1 , the two detection channels are shown as being positioned in the plane of the paper and the illumination subsystem is also shown as being positioned in the plane of the paper. Thus, in this embodiment, the two detection channels are positioned in (e.g., centered in) the plane of incidence. However, one or more of the detection channels may be positioned outside the plane of incidence. For example, the detection channel formed by the light collector 30, the element 32, and the detector 34 may be configured to collect and detect light scattered from the plane of incidence. Thus, such a detection channel may generally be referred to as a "side" channel, and such a side channel may be centered in a plane substantially perpendicular to the plane of incidence.

Although FIG. 1 shows an embodiment of an imaging subsystem including two detection channels, the imaging subsystem may include a different number of detection channels (e.g., only one detection channel or two or more detection channels). In one such example, the detection channel formed by the light collector 30, element 32, and detector 34 may form a side channel as described above, and the imaging subsystem may include an additional detection channel (not shown) formed as another side channel positioned on the opposite side of the incident plane. Thus, the imaging subsystem may include a detection channel that includes the light collector 24, element 26, and detector 28 and is centered in the incident plane and is configured to collect and detect light at (several) scattering angles that are at or near normal to the sample surface. Thus, this detection channel may generally be referred to as a "top" channel, and the imaging subsystem may also include two or more side channels configured as described above. Thus, the imaging subsystem may include at least three channels (i.e., one top channel and two side channels), and each of the at least three channels has its own light collector, each of which is configured to collect light at a scattering angle different from each of the other light collectors.

As described further above, each of the detection channels included in the imaging subsystem can be configured to detect scattered light. Therefore, the imaging subsystem shown in Figure 1 can be configured for dark field (DF) imaging of samples. However, the imaging subsystem may also or alternatively include detection channel(s) configured for bright field (BF) imaging of the sample. In other words, the imaging subsystem may include at least one detection channel configured to detect light specularly reflected from the sample. Therefore, the imaging subsystem described herein can be configured for DF only, BF only, or both DF and BF imaging. Although each of the optical collectors is shown in Figure 1 as a single refractive optical element, each of the optical collectors may include one or more refractive optical elements and/or one or more reflective optical elements.

One or more detection channels may include any suitable detector known in the art, such as photomultiplier tubes (PMTs), charge coupled devices (CCDs), and time-delayed integration (TDI) cameras. The detectors may also include non-imaging detectors or imaging detectors. If the detectors are non-imaging detectors, each of the detectors may be configured to detect certain characteristics of the scattered light (such as intensity), but may not be configured to detect such characteristics that vary depending on position within the imaging plane. Thus, the output generated by each of the detectors included in each of the detection channels of the imaging subsystem may be a signal or data rather than an image signal or image data. In these examples, a computer subsystem (such as computer subsystem 36 of the imaging subsystem) can be configured to generate an image of the sample from the non-imaging output of the detector. However, in other examples, the detector can be configured as an imaging detector configured to generate an imaging signal or image data. Thus, the imaging subsystem can be configured to generate images in a number of ways.

It should be noted that FIG. 1 is provided herein to generally illustrate a configuration of an imaging subsystem that may be included in system embodiments described herein. Obviously, the imaging subsystem configuration described herein can be modified to optimize the performance of the imaging subsystem as is typically performed when designing a commercial imaging system. Additionally, the system described herein may be implemented using an existing system such as the 29xx/39xx series of tools commercially available from KLA (eg, by adding the functionality described herein to an existing detection system). For some such systems, the methods described herein may be provided as optional functionality of the system (eg, in addition to other functionality of the system). Alternatively, the system described herein may be designed "from scratch" to provide an entirely new system.

The computer subsystem 36 may be coupled to the detector of the imaging subsystem in any suitable manner (e.g., via one or more transmission media, which may include "wired" and/or "wireless" transmission media) so that the computer subsystem may receive output generated by the detector. The computer subsystem 36 may be configured to use the output of the detector to perform a number of functions. For example, if the system is configured as an inspection system, the computer subsystem may be configured to use the output of the detector to detect events (e.g., defects and potential defects) on the sample. Detecting events on the sample may be performed as further described herein.

The computer subsystem of the imaging subsystem may be further configured as described herein. For example, the computer subsystem 36 may be part of or may be configured as one or more computer systems described herein. In particular, the computer subsystem 36 may be configured to perform the steps described herein. Thus, the steps described herein may be performed "on tool" by a computer system or subsystem that is part of an imaging subsystem.

The computer subsystem of the imaging subsystem (as well as other computer subsystems described herein) may also be referred to herein as computer system(s). Each of the computer subsystem(s) or system(s) described herein may take a variety of forms, including a personal computer system, video computer, mainframe computer system, workstation, network equipment, Internet equipment, or other device. In general, the term "computer system" can be broadly defined to include any device having one or more processors that execute instructions from a memory medium. The computer subsystem(s) or system(s) may also include any suitable processor known in the art (such as a parallel processor). Additionally, the computer subsystem(s) or system(s) may include a computer platform with high-speed processing and software (either as a stand-alone tool or as a network tool).

If the system includes more than one computer subsystem, the different computer subsystems may be coupled to each other so that images, data, information, instructions, etc. may be sent between the computer subsystems. For example, computer subsystem 36 may be coupled to computer system(s) 102 (as shown by the dashed lines in FIG. 1 ) via any suitable transmission medium, which may include any suitable wired and/or wireless transmission medium known in the art. Two or more such computer subsystems may also be operatively coupled via a common computer-readable storage medium (not shown).

Although the imaging subsystem is described above as an optical or light-based imaging subsystem, in another embodiment, the imaging subsystem is configured as an electron beam imaging subsystem. In an electron beam imaging subsystem, energy directed to the sample includes electrons, and energy detected from the sample includes electrons. In one such embodiment shown in Figure 1a, the imaging subsystem includes an electron column 122, and the system includes a computer subsystem 124 coupled to the imaging subsystem. Computer subsystem 124 may be configured as described above. Additionally, this imaging subsystem may be coupled to another computer system or systems in the same manner as described above and shown in FIG. 1 .

As also shown in Figure 1a, the electron column includes an electron beam source 126 configured to generate electrons that are focused by one or more components 130 onto a sample 128. The electron beam source may include, for example, a cathode source or emitter tip, and the one or more components 130 may include, for example, a gun lens, an anode, a beam limiting aperture, a gate, a beam current selecting aperture, an objective lens, and a scanning subsystem, all of which may include any such suitable components known in the art.

Electrons (eg, secondary electrons) returning from the sample may be focused by one or more elements 132 to detector 134 . One or more components 132 may include, for example, a scanning subsystem, which may be the same scanning subsystem included in component(s) 130 .

The electron column may contain any other suitable components known in the art. Additionally, the electron column can be further configured as described in the following patents: U.S. Patent No. 8,664,594 issued to Jiang et al. on April 4, 2014; U.S. Patent No. 8,692,204 issued to Kojima et al. on April 8, 2014 , U.S. Patent No. 8,698,093 issued to Gubbens et al. on April 15, 2014, and U.S. Patent No. 8,716,662 issued to MacDonald et al. on May 6, 2014, which are incorporated by reference as if set forth in their entirety. in this article.

Although the electron column is shown in Figure 1a configured so that electrons are directed to the sample at one oblique angle of incidence and scattered from the sample at another oblique angle, the electron beam may be directed to and scattered from the sample at any suitable angle. Additionally, as further described herein, the e-beam imaging subsystem can be configured to use multiple modes to generate output of the sample (eg, using different illumination angles, collection angles, etc.). Multiple modes of the e-beam imaging subsystem may differ in any output generation parameters of the imaging subsystem.

Computer subsystem 124 may be coupled to detector 134, as described above. The detector detects electrons returning from the surface of the sample, thereby forming an electron beam image (or other output) of the sample. The electron beam image may include any suitable electron beam image. Computer subsystem 124 may be configured to use the output generated by detector 134 to detect events on the sample, which may be performed as described above or in any other suitable manner. Computer subsystem 124 may be configured to perform any of the additional step(s) described herein. A system including the imaging subsystem shown in Figure 1a may be further configured as described herein.

It should be noted that FIG. 1a is provided herein to generally illustrate a configuration of an electron beam imaging subsystem that may be included in the embodiments described herein. As with the optical imaging subsystem described above, the electron beam imaging subsystem configuration described herein may be modified to optimize the performance of the imaging subsystem as is typically performed when designing a commercial system. In addition, the systems described herein may be implemented using an existing system such as tools commercially available from KLA (e.g., by adding the functionality described herein to an existing system). For some of these systems, the methods described herein may be provided as optional functionality of the system (e.g., in addition to other functionality of the system). Alternatively, the systems described herein may be designed "from scratch" to provide an entirely new system.

Although the imaging subsystem is described above as a light or electron beam imaging subsystem, the imaging subsystem may be an ion beam imaging subsystem. Such an imaging subsystem may be configured as shown in Figure 1a, except that the electron beam source may be replaced by any suitable ion beam source known in the art. Additionally, the imaging subsystem may include any other suitable ion beam imaging system, such as those included in commercially available focused ion beam (FIB) systems, helium ion microscopy (HIM) systems, and secondary ion mass spectrometry (SIMS) systems. .

As described further above, the imaging subsystem is configured to have multiple modes. Generally speaking, a "mode" can be defined by parameter values of the imaging subsystem used to generate the output of the sample. Accordingly, different modes may differ in the value of at least one of an optical or electron beam parameter of the imaging subsystem (other than the location on the sample where the output is generated). For example, for a light-based imaging subsystem, different modes may use different wavelengths of light. As further described herein (eg, by using different light sources, different spectral filters, etc. for different modes), the modes can differ in the wavelength of light directed to the sample. In another embodiment, different modes may use different illumination channels. For example, as mentioned above, the imaging subsystem may include more than one illumination channel. Thus, different lighting channels can be used in different modes.

Multiple modes may also differ in lighting and/or collection/detection. For example, as described further above, the imaging subsystem may include multiple detectors. Thus, one of the detectors can be used in one mode and the other of the detectors can be used in another mode. Furthermore, modes may differ from each other in one or more ways described herein (eg, different modes may have one or more different lighting parameters and one or more different detection parameters). The imaging subsystem may be configured to scan a sample using different modes in the same scan or in different scans, for example, depending on the ability to scan the sample using multiple modes simultaneously.

The outputs generated in different modes can be aligned with each other, as further described herein. For example, images generated in different modes can be aligned with each other so that images generated at the same location on the sample can be used together for detection. In other examples, outputs generated in different modes for the same location can be aligned with each other so that the results of any defect detection performed using the outputs generated in the different modes can be aligned with each other. For example, outputs generated using different modes can be aligned with each other so that the results of defect detection (e.g., defect candidates) detected using different modes are aligned with each other. In this way, the results of the alignment can be easily used to determine the results that spatially overlap with each other on the sample across different modes.

In one embodiment, the imaging subsystem is an inspection subsystem. In this way, the system described herein can be configured as an inspection system. However, the system described herein can be configured as another type of semiconductor-related quality control type system, such as a defect inspection system and a metrology system. For example, the embodiments of the imaging subsystems described herein and shown in Figures 1 and 1a can be modified in one or more parameters to provide different imaging capabilities depending on the application in which they will be used. In one embodiment, the imaging subsystem is configured as an electron beam defect inspection subsystem. For example, if the imaging subsystem shown in Figure 1a is to be used for defect inspection or metrology rather than for inspection, it can be configured to have a higher resolution. In other words, the embodiments of the imaging subsystems shown in FIGS. 1 and 1a describe some general and various configurations of an imaging subsystem that can be customized in a number of ways that will be apparent to those skilled in the art to produce imaging subsystems with different imaging capabilities that are more or less suitable for different applications.

As described above, the imaging subsystem may be configured to direct energy (eg, light, electrons) to and/or scan energy across a physical version of the sample, thereby producing a physical version of the sample. actual image. In this way, the imaging subsystem can be configured as a "real" imaging system rather than a "virtual" system. However, a storage medium (not shown) and the computer subsystem(s) 102 shown in Figure 1 can be configured as a "virtual" system. In particular, the storage media and computer subsystem(s) are not part of the imaging subsystem 100 and do not have any capability for handling physical versions of the samples but may be configured to perform similar detections using the stored detector outputs. It has the function of a virtual detector, a virtual weights and measures system that performs functions similar to weights and measures, a virtual defect inspection tool that performs functions similar to defect inspection, etc. Systems and methods configured as "virtual" systems are described in commonly assigned U.S. Patent Nos. 8,126,255 to Bhaskar et al. issued on February 28, 2012, and Duffy et al. issued on December 29, 2015. No. 9,222,895 and U.S. Patent No. 9,816,939 issued to Duffy et al. on November 14, 2017, which are incorporated herein by reference as if set forth in their entirety. The embodiments described herein may be further configured as described in these patents. For example, one or more of the computer subsystems described herein may be further configured as described in these patents.

The system includes one or more computer systems, which may include any configuration of any of the computer subsystem(s) or system(s) described above. One or more computer systems are configured to separately align the first image and the second image to a design of the sample. In this manner, inter-modal image alignment can utilize alignment-to-design algorithms such as those available from KLA and described in Kulkarni's above-referenced patent to align images of multiple modalities to a design coordinate system. Combining the first image and the second image can also be performed as described in U.S. Patent No. 9,830,421 issued to Bhattacharyya et al. on November 27, 2017, and U.S. Patent No. 10,698,325 issued to Brauer et al. on June 30, 2020. These patents are hereby incorporated by reference to the same extent as if set forth in their entirety. The embodiments described herein may be further configured as described in these patents. This step can also be performed as described further herein.

In one embodiment, the imaging subsystem is configured to generate a first setup image of the sample using a first mode, and one or more computer systems are configured to: select a first setup alignment target in the first setup image; generate a first presentation image from a design of the first setup alignment target; align the first presentation image to a portion of the first setup image corresponding to the first setup alignment target; and determine a first setup design-to-image offset for the first setup alignment target. For example, as shown in step 200 of FIG. 2a, the imaging subsystem may generate a first setup image by scanning the entire die using a light beam (or another energy source described herein). Generating the first setup image may include scanning the entire die or any other suitable repeating structure (such as a field) on the sample. Scanning may be performed as further described herein.

Next, one or more computer systems may find unique targets in the first setup image (first setup alignment target), as shown in step 202. The unique target may be unique in any suitable manner known in the art, which renders the target suitable for alignment purposes. For example, the unique target may be a patterned feature having a unique shape relative to other patterned features within a predetermined search window (such as an image frame or workpiece), patterned features having a unique spatial relationship relative to each other within the predetermined search window, etc. Although it may be practical to select multiple unique targets in the first setup image, in general, any one or more unique targets may be selected in the first setup image. Each of the unique targets may be different from each other in any unique manner. In addition, the unique targets may include more than one instance of the same unique target.

As shown in step 204, one or more computer systems may receive designs for each of the unique target(s). The one or more computer systems may receive the designs in any suitable manner, such as by searching for a design for the sample based on information of the unique target(s) collected from the first setting image, by requesting a portion of a design (e.g., a design clip) from a storage medium containing the designs or the computer system at the location(s) of the unique target(s), etc. The designs received by the one or more computer systems may include any of the designs, design data, or design information described further herein.

As shown in step 206, one or more computer systems may generate a first rendered image from the design. Generating the first rendered image may be performed in any suitable manner. For example, based on a design clipping of unique target(s) from design data for one or more layers on the sample, the design layer(s) may be rendered and the resulting simulated image(s) may be used as further described herein. The embodiments described herein may also use rendered images of possible alignment targets and compare them to the first set image alignment target position images to select the best subset of unique target(s) for use, as further described herein.

The first presentation image may be generated by one or more components (such as a model, software, hardware, and the like executed by one or more computer systems). In some examples, the one or more components may perform a forward simulation of the processes involved in manufacturing (several) design layers on a sample. For example, the simulated image may include simulating the appearance of (several) design layers when printed on a sample. In other words, the presentation or simulation image may include generating a simulated representation of a sample with (several) design layers printed thereon. An example of an empirically trained process model that can be used to generate a simulated sample is included in SEMulator 3D, which is commercially available from Coventor, Inc. of Cary, North Carolina. An example of a rigorous lithography simulation model is Prolith, which is commercially available from KLA and can be used in conjunction with the SEMulator 3D product. However, any suitable model(s) of any of the process(es) involved in producing an actual sample from a design can be used to produce a simulated sample. In this way, a design can be used to simulate how a sample would appear in sample space (not necessarily how such a sample would appear to an imaging system) upon which corresponding design layer(s) have been formed. Thus, a simulated representation of a sample can represent how the sample would appear in 2D or 3D space of the sample.

The simulated representation of the sample can then be used to generate rendering image(s) that represent how the unique object(s) would appear in the first mode image of the sample. These renderings can be generated using a model such as WINsim, which is commercially available from KLA and which rigorously models the response of a detector using an electromagnetic (EM) wave solver. Such simulations may be performed using any other suitable software, algorithm(s), method(s) or system(s) known in the art.

In other examples, one or more components may include a deep learning (DL) model configured to infer (several) rendered images from a design. In other words, one or more components may be configured to transform (by inferring) one or more design files into one or more rendered images to be generated for a sample using a first model. One or more components may include any suitable DL model or network known in the art, including, for example, a neural network, a CNN, a generative model, etc. One or more components may also be configured as described in the following: U.S. Patent Application Publication No. 2017/0140524, co-owned by Karsenti et al., published on May 18, 2017; U.S. Patent Application Publication No. 2017/0148226, co-owned by Zhang et al., published on May 25, 2017; U.S. Patent Application Publication No. 2017/0193400, co-owned by Bhaskar et al., published on July 6, 2017; U.S. Patent Application Publication No. 2017/0193400, co-owned by Zhang et al., published on July 6, 2017 No. 2017/0193680, jointly owned by Bhaskar et al., published on July 6, 2017; No. 2017/0194126, jointly owned by Bhaskar et al., published on July 13, 2017; No. 2017/0200260, jointly owned by Bhaskar et al., published on July 13, 2017; No. 2017/0200264, jointly owned by Park et al., published on July 13, 2017; No. 2017/0200265, jointly owned by Bhaskar et al., published on July 13, 2017; U.S. Patent Application Publication No. 2017/0200265, jointly owned by Zhang et al., published on November 30, 2017; U.S. Patent Application Publication No. 2017/0345140, jointly owned by Zhang et al., published on December 7, 2017; U.S. Patent Application Publication No. 2018/0107928, jointly owned by Zhang et al., published on April 19, 2018; U.S. Patent Application Publication No. 2018/0345140, jointly owned by Zhang et al., published on November 30, 2017; U.S. Patent Application Publication No. 2017/0351952, jointly owned by Zhang et al., published on December 7, 2017; U.S. Patent Application Publication No. 2018/0107928, jointly owned by Zhang et al., published on April 19, 2018; U.S. Patent Application Publication No. 2018/0351953, jointly owned by Zhang et al., published on October 11, 2018 U.S. Patent Application Publication No. 2018/0293721 to Ha et al., co-owned U.S. Patent Application Publication No. 2018/0330511 to Ha et al., published on November 15, 2018; U.S. Patent Application Publication No. 2019/0005629 to Dandiana et al., published on January 3, 2019; and U.S. Patent Application Publication No. 2019/0073568 to He et al., published on March 7, 2019, which are incorporated herein by reference as if fully set forth. The embodiments described herein may be further configured as described in such patent application publications. Additionally, the embodiments described herein may be configured to perform any of the steps described in these patent application publications.

As shown in step 208, one or more computer systems may perform alignment of the first rendered image and the first set image at each unique target. Alignment of the first rendered image and the first set image may be performed as further described herein or in any other suitable manner known in the art. As shown in step 210, one or more computer systems may determine a first set of design-to-image offsets for each alignment frame (ie, each image frame that contains an instance of an alignment target). The first set design-to-image offset may be determined in any suitable manner and expressed in any suitable manner (eg, as a Cartesian offset, as a two-dimensional function, etc.).

Based on the alignment results of the first presented image and the first set image, one or more computer systems may determine the suitability of the first set alignment target for use in the embodiments described herein. For example, if it is not possible to align one of the set alignment targets to the first presented image of the set alignment target, the set alignment target may be rejected. In this way, multiple first set alignment targets may be selected and considered by the embodiments described herein, and only a portion of the alignment targets may be selected for use, as further described herein. In addition, more than one set alignment target may be selected for use in the embodiments described herein, and one or more set alignment targets may be selected in each test image portion of the first image that will be aligned to the design as described herein. For example, the embodiments described herein may attempt to select at least one alignment target for each frame image in the first image.

The above process may be performed by the system for all (or two or more) modes, and one or more computer systems may generate a database having alignment frame images and their offsets for each mode. For example, in one such embodiment, the imaging subsystem is configured to generate a second setup image of the sample using the second mode, and the one or more computer systems are configured to: select a second setup alignment target in the second setup image; generate a second rendered image from the design of the second setup alignment target; align the second rendered image to a portion of the second setup image corresponding to the second setup alignment target; and determine a second setup design-to-image offset for the second setup alignment target. Each of these steps may be performed as further described above. In this way, the embodiments described herein may be configured to align images of different modes with each other using a block-to-design approach.

For a location of interest in the first image, one or more computer systems are configured to generate a first difference image of the location of interest by subtracting a first reference image of the location of interest from a test image portion of the first image of the location of interest. The first reference image may be subtracted from the test image portion of the first image in any suitable manner. The first reference image may include any suitable reference image, such as an image generated by the imaging subsystem at a location on the sample corresponding to the location of interest (i.e., an image from an adjacent die on the sample), a reference image from a database or another storage medium, a reference image presented from a design and stored in a storage medium, and the like.

Before subtracting the first reference image from the test image portion of the first image, the first reference image and the test image portion may be aligned with each other or to a common reference. For example, in one embodiment, before generating a first difference image based on separately aligning the first image to the design, the first reference image and the test image portions of the first image are aligned with each other. In one such example, a reference image generated from the sample can be aligned to a design of the sample as described herein. Therefore, when aligning the first image to a design as described herein, the first reference image and the test portion of the first image are aligned to a common reference (the design) and are therefore effectively aligned with each other based on the design coordinates. In another such example, the reference image may be part of the design or may be present from the design and thus inherently aligned to the design. In this manner, the first reference image and the test portion of the first image can also be aligned to a common reference (design) by separately aligning the first image to the design. In a further example, the first reference image and the test portion of the first image can be directly aligned with each other (this can be performed as described herein), and then subtracted from each other.

In one embodiment, the location of interest is a location of a defect detected in the first image, and the imaging subsystem is configured as a detection subsystem. For example, if the imaging subsystem is a detection subsystem, and if the alignment described herein is performed for detection of a sample, first difference images may be generated for a plurality of locations of interest on the sample (e.g., detection areas on the sample) as described herein and then defect detection may be performed using the first difference images. Defect detection may be performed as further described herein. Thus, the first difference image may be generated before the location of interest for which the steps described herein are performed is known. Thus, the location of interest for which the steps described herein are performed may be one of the locations for which a defect is detected using the first difference image. In this way, a first difference image can be generated before identifying the location of interest for which the steps described herein are performed. In addition, the steps described herein can be performed for multiple locations of interest, and a defect can be detected at each of the multiple locations of interest. However, in other examples (such as metrology and defect inspection), the location of interest may be known in advance (e.g., from a metrology or defect inspection sampling plan) before the first difference image is generated. In this way, a first difference image can be generated for a location of interest that is known a priori. As further described herein, for some applications such as inspection, the additional steps described herein may be performed only for some locations for which the first difference image is generated (e.g., only for the locations of defects detected on the sample).

In another embodiment, one or more computer systems are configured to determine a region of interest in the test image portion of the first image based on the first run-time design-to-image offset, perform defect detection in the region of interest, and designate a location of a defect detected by the defect detection as the location of interest. For example, the one or more computer systems may determine the placement of the region of interest in the test image portion of the first image by performing an alignment with the design of the first run-time image.

In one such example, one or more computer systems may be configured to perform alignment of a set alignment frame in Mode 1 with a first image (runtime alignment frame), as shown in step 212 of Figure 2b displayed in. The set alignment frame may be a frame image from the first set image at the location of one of the first set alignment targets. This alignment may be performed as described herein or in any other suitable manner known in the art. One or more computer systems may also determine the offset between the set alignment frame of Mode 1 and the first image, as shown in step 214 . Additionally, one or more computer systems may determine the offset between the design of Mode 1 and the first image, as shown in step 216 . These offsets may be determined in any suitable manner known in the art and may have any format known in the art.

As shown in step 218, one or more computer systems may determine a region of interest in the first image based on offset correction in Mode 1. Determining the region of interest in the first image may include using the location of the region of interest in the design (which should be known a priori from another method or system) and the offset between the design of Mode 1 and the first image to separate the region of interest. placed in the first image. In other words, if the location of the area of interest is known in the design coordinates and the first image has been aligned to the design as described above, the location of the area of interest in the first image can be easily determined. The region of interest may be any suitable region of interest known in the art, may be generated in any suitable manner known in the art, and may have any suitable format known in the art. For example, the area of interest may be one of a plurality of areas of interest determined from the design and may cover a user's area of interest.

Next, one or more computer systems may perform a defect inspection (wafer scan), as shown in step 220 . Defect detection may be performed in any suitable manner, such as by applying a threshold to the difference image. Locations or areas in the difference image that are greater than the threshold value may be identified as defects (or potential defects), and locations or areas in the difference image that are less than the threshold value may not be identified as potential defects or defects. Defect inspection may also be performed using any suitable defect detection method or algorithm known in the art, such as the MDAT defect detection algorithm used by some inspection tools commercially available from KLA. The location of the defect may then be determined in any suitable manner known in the art (e.g., using differential or test images). The location of the defect may be determined relative to the sample or design based on the image itself or the offsets described herein. ). Next, a location of one of the defects or potential defects may be designated as a location of interest for one of the steps described herein.

The one or more computer systems are further configured to generate a second difference image of the location of interest by subtracting a second reference image of the location of interest from a test image portion of the second image of the location of interest. The second difference image may be generated using only different test and reference images as described further above. The reference image used to generate the second difference image may be any of the reference images described above but generated for the second mode rather than the first mode. In other words, different reference images can be used to generate differential images for different modes (regardless of whether the differential images are generated in the same or different ways).

In one embodiment, separately aligning the second image to the design is performed only for a portion of the second image corresponding to the location of a defect detected by defect detection. For example, as shown in step 222, for each detected defect using mode 1, one or more computer systems can perform set to run-time frame offset calculations for modes 2 through n. In this way, defects can be detected in a first mode, and the location of the defect can be designated as a location of interest as described above. Then, for any location of a defect, the second image can be aligned to the design only for the portion of the second image corresponding to the location of the defect, which can be performed as described herein. Furthermore, although separate alignment is described herein as being performed for a location of interest, separate alignment for images generated using the second mode may be performed for any one or more locations of interest.

In another embodiment, one or more computer systems are configured to perform the separate alignment for a first image, determine a location of interest in the first image, and perform the separate alignment for a second image based on the determined location of interest. For example, determining the location of interest in the first image may be performed by aligning the first image to a design as described herein and then performing defect detection using the first image. Aligning the second image to the design may then be performed only for the locations of interest corresponding to one or more of the defects detected as described above. The location(s) of interest may also not correspond to a defect. For example, in these embodiments, the (several) locations of interest may also be locations where metrology is performed, locations where metrology performed using the first image produces an abnormal result, locations where a defect is re-detected during defect review, and the like. In this way, a first image generated using a first mode can be aligned to a design, one or more locations of interest can be determined in the first image based on the results of the alignment step, and then for any one or more of the locations of interest, a second image generated using a second mode can be aligned to the design. Aligning the (several) second images to the design for the (several) locations of interest can be performed for a number of reasons described herein (e.g., generating a differential image for the (several) locations of interest and information to determine the (several) locations, detecting a defect at the (several) locations, measuring a patterned feature for the (several) locations, and the like).

One or more computer systems are also configured to align the first difference image and the second difference image with each other. For example, as shown in step 224 of Figure 2c, one or more computer systems can use offset correction images of modes 1 to mode n. Offset correction images for each of the modes can be generated as described herein. One or more computer systems can also calculate difference images from test and reference images of modes 1 to n, as shown in step 226 of Figure 2c. As shown in step 228 of Figure 2c, one or more computer systems can also align the difference images of mode 1 and mode 2, mode 1 and mode 3, ..., mode 1 and mode n for each image set to calculate the alignment offset. In this way, the embodiments described herein can be configured to use difference images generated from two different modes and align them with each other. Aligning the difference images with each other may be performed as further described herein and provides several advantages as further described herein.

In one embodiment, aligning the first difference image and the second difference image with each other includes aligning noise in the first difference image to noise in the second difference image. For example, original images generated using different modes may be difficult to align with each other because some structures may not be present in each of the multi-mode images, some structures may be inverted at their equal contrast, or have different grayscale. In one such example, as shown in FIG. 3, a test image (300) of mode 1 and a reference image (302) of mode 1 appear substantially different from a test image (304) of mode 2 and a reference image (306) of mode 2. Specifically, the test and reference images generated using mode 1 and the test and reference images generated using mode 2 shown in FIG. 3 may be generated for the same location on a sample, but as can be seen from FIG. 3, the images have inverted grayscale. Specifically, areas with relatively darker gray in the test and reference images of Mode 1 have relatively lighter gray in the test and reference images of Mode 2. The same is true for relatively lighter gray in the test and reference images of Mode 1 and relatively darker gray in the test and reference images of Mode 2.

However, when differential images are generated for multiple modes, the process of generating differential images for different modes can actually reduce or even eliminate many or even all differences between the mode images that make inter-mode image alignment difficult. For example, difference image 308 may be generated from test image 300 and reference image 302 by Mode 1 image subtraction that may be performed as described herein. Additionally, difference image 310 may be generated from test image 304 and reference image 306 by mode 2 image subtraction that may be performed as described herein. As can be seen from difference images 308 and 310, the inverted gray scale at corresponding locations in the test and reference images of Mode 1 and Mode 2 has been eliminated from the difference images through image subtraction. The remaining noise in the difference images shown by the dotted lines in these images can then be used for image alignment. In particular, the remaining noise in the two difference images can be used to align an image from the first mode to an image from the second mode. Thus, difference images can be used to align images of different modes. Additionally, differential image noise can be used for image alignment. Differential image noise can be used for image alignment as described herein or in any other suitable manner. For example, differential image noise can be treated like any other image feature in an image alignment process.

In some embodiments, aligning the first difference image and the second difference image with each other is performed based on a normalized sum of squared differences (NSSD). For example, step 228 of FIG. 2c may be performed using NSSD of the difference images of mode 1 and mode 2, mode 1 and mode 3, ..., mode 1 and mode n for each image set to calculate the alignment offset. NSSD may be performed using any suitable method, algorithm, function, etc. known in the art.

The one or more computer systems are further configured to determine information about the location of interest from the results of aligning the first difference image and the second difference image with each other. For example, there are various information that can be determined from the difference image alignment results. As further described herein, this information includes information about the degree to which the pattern image has been aligned to a design and therefore a common reference, information about the location of interest determined from multiple difference images or other images that have been verified and/or calibrated for alignment by difference image alignment, information about the pattern itself that can be used for pattern selection and recipe setting, and the like.

In one embodiment, the determination information includes verifying whether the separate alignment is accurately performed. For example, the difference images of each mode can be used to verify the performance of the alignment between modes. In this way, the embodiments described herein can be configured to use the difference images to verify the design-based alignment. Specifically, as further described herein, the mode image is aligned to a design before the difference image is generated. Therefore, when the difference images from different modes are aligned with each other, if the design to image process is successful, there should be no alignment offset between the design coordinates of the difference images. In other words, after the difference images are aligned with each other, the alignment positions in the difference images should have the same design coordinates. If the alignment locations in the difference images do not have the same design (or other common reference) coordinates, then there is some marginality in one or more of the design-to-image alignment procedures for one or more of the patterns.

Of course, in practice, the offset between the alignment positions in the difference images need not be exactly zero to verify the separate alignment as accurate. Instead, there may be some acceptable tolerance in the alignment offset between the difference images that can be taken into account when determining the verification. This acceptable tolerance can be quantified by a threshold value further described herein.

In some embodiments, verification includes determining an alignment offset between the first difference image and the second difference image and comparing the alignment offset to a predetermined threshold value. For example, as shown in step 230, one or more computer systems may determine whether the alignment offset is greater than a threshold value. This alignment offset may be determined as further described herein. The predetermined threshold value may be determined based on acceptable values for the alignment offset. Therefore, the predetermined threshold value may respond to acceptable margins that are specific to individual models and designed into the image alignment process. Thus, the predetermined threshold value may vary depending on factors such as the type of sample, the application for which the alignment is performed, the performance required by the user of the alignment process, and the like. An example of a suitable threshold value may be greater than or equal to one pixel in one or both dimensions. The threshold value may have any suitable format known in the art, which may vary depending on the format of the alignment offset. For example, the threshold value may be expressed as a function of one or two dimensions, etc.

In another embodiment, when the separate alignment is verified to be performed accurately, the determination information includes one or more attributes of a defect at the location of interest determined from the first difference image and the second difference image. For example, as shown in step 232 of Figure 2c, if the alignment offset is no greater than a critical value, one or more computer systems may calculate the image-based attributes. In this way, the embodiments described herein enable defect attributes to be determined from multi-modal images that are aligned with each other within a predetermined accuracy. In other words, the embodiments described herein can substantially ensure that the defect attributes determined from images generated using different modes are determined at the actual location of the defect in the multi-modal image. The defect attributes determined from the multi-modal images may include any defect attributes known in the art, such as defect size, defect shape, defect roughness, defect orientation, and the like. Additionally, the defect attributes determined from different multi-mode images may be the same defect attribute or different defect attributes. For example, defect size may be determined separately from each of two or more multi-mode images. In another example, defect size may be determined from one of the two or more multi-mode images, and defect roughness may be determined from another of the two or more multi-mode images. Regardless of determining the same or different defect attributes from the multi-mode images, multiple defect attributes may be combined for one or more applications, such as defect classification, defect verification, defect filtering, and the like.

For applications other than detection, information about the location of interest may be determined separately from different modal images and used together or separately. For example, for an application such as metrology, when the location of interest is successfully located in a multi-modal image, a property or characteristic of the location of interest may be determined from each of two or more multi-modal images. For example, one of the modal images may be used to determine a size of a patterned feature or layer at the location of interest, and another of the modal images may be used to determine a roughness of the patterned feature or layer.

In an additional embodiment, when the separate alignment is not verified to be accurately performed, the determination information includes determining one or more corrections to at least one of separately aligning the first image and the second image to the design and aligning the first difference image and the second difference image to each other. For example, if the alignment offset between the difference images is too large (e.g., greater than a predetermined threshold value), it can be corrected using an offset derived from the difference image alignment. In one such example, as shown in step 234 of FIG. 2c, if the alignment offset is greater than a threshold value, the one or more computer systems can adjust the alignment offset. In this way, the embodiments described herein can be configured for correcting the design-based alignment using the difference images. Correcting the design-based alignment can also be performed in any suitable manner known in the art.

In this manner, embodiments described herein can align two (or more) images derived from different modes with each other. For example, as described above, separately aligning images from different modes to a design should theoretically result in images from multiple modes being aligned to a common reference and thus to each other. However, this alignment is not always successful, especially where today's applications such as inspection, metrology and inspection require sufficient accuracy. Inaccuracies can arise from sources that are difficult to eliminate, such as marginality in the image presented by the design, difficulty in selecting one(s) of unique alignment targets from the modeled image, marginality in the alignment to the design algorithm, etc. However, by aligning the difference images generated from multiple modes with each other, embodiments described herein can perform a direct difference-image alignment, which can be used as described above to determine whether verification is performed separately for different modes. Regarding the alignment of the design, whether the alignment is not within acceptable accuracy requirements (e.g., determined by comparison with predetermined thresholds) and whether the alignment has not been verified to be sufficiently accurate; regarding the alignment results (e.g., for One or more corrections are made (one or more of the alignment offsets) to thereby correct the alignment accuracy.

One or more computer systems may be configured to execute one or more of the sample, imaging subsystem, or another sample, process, or tool using the results of the defect detection step, the determination information step, and any other steps described herein. Function. For example, results generated by one or more of the computer systems described herein may include information about any defects detected on the sample (such as the location of the bounding box of the detected defects, detection scores), information about the defects Classification information (such as a class label or ID, any defect attributes determined from any one of multiple modes, multi-mode defect images, etc.) or any such suitable information known in the art.

Results for defects and/or locations of interest may be generated by the computer system(s) and/or imaging subsystem in any suitable manner. Results for defects and/or locations of interest may be in any suitable form or format, such as a standard file type. The computer system(s) and/or imaging subsystem may generate the results and store the results so that the results may be used by the computer system(s) and/or another system or method to perform one or more functions on the sample or another sample of the same type. Such functions include, but are not limited to, a procedure to change a process or step to be performed on the sample, such as in a feedback manner, a procedure to change a process or step to be performed on the sample, such as in a feedforward manner, etc. For example, due to the relatively high accuracy inter-modal image alignment achieved by the embodiments described herein, the embodiments described herein may allow detection procedures and tools to detect certain DOIs with increased sensitivity. This increased sensitivity to certain DOIs allows users to improve their ability to make correct processing decisions.

The computer system(s) may also be configured to store the determined information in any suitable computer-readable storage medium. The information may be stored with any of the results described herein and may be stored in any manner known in the art. The storage medium may include any storage medium described herein or any other suitable storage medium known in the art. After the information has been stored, the information may be accessed in the storage medium and used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method or system, etc. For example, the embodiments described herein may generate a test recipe, as further described herein. The test recipe may then be stored and used by the system or method (or another system or method) to test the sample or other samples to thereby generate information (e.g., defect information) of the sample or other samples.

The embodiments described herein can also be used to set up an image-based process, such as inspection, defect inspection, weights and measures, etc. For example, although embodiments are described herein for applications in which a mode has been previously selected and known, in some instances, the embodiments described herein can be used to align images from different modes with each other such that the images can be evaluated and therefore the usefulness of the pattern for a particular application. In one such example, images from different modalities can be aligned with each other as described herein, and each of the images can then be evaluated for their usefulness in performing a procedure such as inspection, defect inspection, metrology, etc. For example, whether a particular feature or defect can be detected in each of the images from the different modalities that have been aligned with each other can be used to determine whether each of the different modalities can be used for defect detection or patterned feature measurement. Additionally, images from different modalities that have been aligned with each other can be evaluated to determine defect attributes or pattern feature properties that can be determined from them at a location of interest. In this manner, useful and/or mutually complementary modes can be identified based on inter-mode image alignment. As described above, mode selection is an often tedious and difficult process. Having the ability to substantially precisely align images from different modalities provided by the embodiments described herein provides the process with significant advantages, such as reduced time to results, increased robustness, and comparison of the resulting multi-modal procedures. Best performance, etc.

The embodiments described herein may implement mode selection as described in U.S. Patent No. 10,115,040 issued to Brauer on October 30, 2018, U.S. Patent Application Publication No. 2020/0193588 issued to Brauer et al. on June 18, 2020, and U.S. Patent Application Serial No. 16/883,794 filed by Gaind et al. on May 26, 2020, which are incorporated herein by reference as if fully set forth. The embodiments described herein may be further configured as described in these references.

Each of the embodiments of the system described above can be combined together into a single embodiment. In other words, unless otherwise stated herein, a system embodiment is not mutually exclusive with any other system embodiment.

Another embodiment relates to a method for aligning images of a sample produced using different modes of an imaging subsystem. The method includes using a first mode and a second mode of an imaging subsystem to generate a first image and a second image of a sample, respectively. The method also includes separately aligning the first image and the second image to a design as described above, generating a first difference image, generating a second difference image, and aligning the first difference image and the second difference image with each other. and the steps to determine information. The steps are performed by one or more computer systems that may be configured in accordance with any of the embodiments described herein.

Each of the steps of the method may be performed as further described herein. The method may also include any other step(s) that may be performed by the imaging subsystem and/or computer system(s) described herein. In addition, the method described above may be performed by any of the system embodiments described herein.

An additional embodiment relates to a non-transitory computer-readable medium storing program instructions executable on a computer system to perform a computer-implemented method for aligning images of a sample generated using different modes of an imaging subsystem. One such embodiment is shown in FIG4. Specifically, as shown in FIG4, a non-transitory computer-readable medium 400 includes program instructions 402 executable on a computer system 404. The computer-implemented method may include any step(s) of any method(s) described herein.

Program instructions 402 for implementing methods such as those described herein may be stored on computer-readable media 400. The computer-readable medium may be a storage medium such as a magnetic or optical disk, a magnetic tape, or any other suitable non-transitory computer-readable medium known in the art.

Program instructions may be implemented in any of a variety of ways, including procedural, component-based, and/or object-oriented technologies, etc. For example, program instructions may be implemented using ActiveX controls, C++ objects, JavaBeans, Microsoft Foundation Classes ("MFC"), SSE (Streaming SIMD Extensions), or other technologies or methodologies, as desired.

Computer system 404 may be configured according to any of the embodiments described herein.

In view of this description, further modifications and alternative embodiments of the various aspects of the present invention will be appreciated by those skilled in the art. For example, methods and systems are provided for aligning images of a sample produced using different modes of an imaging subsystem. Therefore, this description is to be construed as merely illustrative and for the purpose of teaching those skilled in the art the general manner of practicing the present invention. It should be understood that the forms of the present invention shown and described herein should be considered the presently preferred embodiments. As will be appreciated by those skilled in the art after having the benefit of this description of the present invention, elements and materials may be substituted for those illustrated and described herein, portions and procedures may be reversed, and certain attributes of the present invention may be utilized independently. Changes may be made to the elements described herein without departing from the spirit and scope of the invention as described in the following claims.

14:Sample 16:Light source 18:Optical components 20:Lens 22:Carrying stage 24:Light collector 26:Component 28:Detector 30:Light collector 32:Component 34:Detector 36: Computer subsystem 100:Imaging subsystem 102: Computer system/computer subsystem 122:Electron column 124: Computer subsystem 126: Electron beam source 128:Sample 130:Component 132:Component 134:Detector 200: steps 202:Step 204:Step 206:Step 208:Step 210: Step 212: Step 214: Step 216:Step 218:Step 220:Step 222:Step 224:Step 226:Step 228:Step 230:Step 232:Step 234:Step 300: Test image of mode 1 302: Reference image of mode 1 304: Test image of mode 2 306: Reference image of mode 2 308:Difference image 310:Difference image 400: Non-transitory computer-readable media 402: Program command 404:Computer system

Those skilled in the art will become aware of further advantages of the present invention with the benefit of the following detailed description of preferred embodiments and after reference to the accompanying drawings, in which: FIGS. 1 and 1a are schematic diagrams showing side views of embodiments of a system configured as described herein; FIGS. 2a to 2c are schematic diagrams showing methods that may be performed to align different modes of a sample produced using an imaging subsystem. 3 is a schematic diagram showing the difference between an image of a sample generated using different modes of an imaging subsystem and a difference image generated for the different modes; and 4 is a block diagram showing an embodiment of a non-transitory computer-readable medium storing program instructions for causing a computer system to execute a computer implementation method described herein. Although the present invention is susceptible to various modifications and alternative forms, specific embodiments of the present invention are shown in the drawings by way of example and described in detail herein. The drawings may not be drawn to scale. It should be understood, however, that the drawings and their detailed description are not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

14:Sample

16:Light source

18:Optical components

20: Lens

22: Stage

24:Light collector

26:Component

28: Detector

30:Light collector

32:Component

34: Detector

36: Computer subsystem

100: Imaging subsystem

102: Computer system/computer subsystem

Claims (19)

A system configured for aligning images of a sample generated using different modes of an imaging subsystem, comprising: the imaging subsystem configured to respectively use a first mode of the imaging subsystem and a second mode producing a first image and a second image of the sample; and one or more computer systems configured to separately align the first image and the second image to the sample A design; for a position of interest in the first image, the position of interest is generated by subtracting a first reference image of the position of interest from a test image portion of the first image of the position of interest. a first difference image of a location; generating a second difference image of the location of interest by subtracting a second reference image of the location of interest from a test image portion of the second image of the location of interest; Aligning the first difference image and the second difference image with each other; and determining information of the position of interest from a plurality of results of aligning the first difference image and the second difference image with each other, wherein determining the information Including verifying that the separate alignment is performed accurately. The system of claim 1, wherein aligning the first difference image and the second difference image with each other includes aligning noise in the first difference image to noise in the second difference image. A system as claimed in claim 1, wherein aligning the first difference image and the second difference image with each other is performed based on a normalized sum of squared differences. A system as claimed in claim 1, wherein the verification comprises: determining an alignment offset between the first difference image and the second difference image; and comparing the alignment offset with a predetermined threshold value. The system of claim 1, wherein when the separate alignment is verified to be accurately performed, determining the information further includes determining one or more attributes of a defect at the location of interest from the first difference image and the second difference image. The system of claim 1, wherein when the separate alignment is not verified to be accurately performed, determining the information further includes determining one or more corrections to at least one of the separate alignment of the first image and the second image to the design and the alignment of the first difference image and the second difference image to each other. A system as claimed in claim 1, wherein the location of interest is a location of a defect detected in the first image, and wherein the imaging subsystem is further configured as a detection subsystem. The system of claim 1, wherein the imaging subsystem is further configured to generate a first setup image of the sample using the first mode, and wherein the one or more computer systems are further configured to: select a first setup alignment target in the first setup image; generate a first rendered image from the design of the first setup alignment target; align the first rendered image to a portion of the first setup image corresponding to the first setup alignment target; and determine a first setup design-to-image offset for the first setup alignment target. The system of claim 8, wherein the imaging subsystem is further configured to generate a second setting image of the sample using the second mode, and wherein the one or more computer systems are further configured to: in the Select a second setting alignment target from the second setting image; generate a second rendering image from the design of the second setting alignment target; align the second rendering image to correspond to the second setting alignment target a portion of the second setting image; and determining a second setting design-to-image offset for the second setting alignment target. The system of claim 8, wherein the separately aligning includes: aligning a set alignment frame image in the first set image of the first set alignment target to a corresponding image in the first image frame image; determine a first inter-image offset between the set alignment frame image and the corresponding frame image; and determine the first inter-image offset and the first set design-to-image offset. A first runtime design-to-image offset between the corresponding frame image and the design. The system of claim 10, wherein the one or more computer systems are further configured to determine a region of interest in the test image portion of the first image based on the first run-time design to image offset, perform defect detection in the region of interest, and designate a location of a defect detected by the defect detection as the location of interest. The system of claim 11, wherein separately aligning the second image to the design is performed only for a portion of the second image corresponding to the location of the defect detected by the defect detection. The system of claim 1, wherein the one or more computer systems are further configured to execute For the separate alignment of the first image, the location of interest in the first image is determined, and the separate alignment of the second image is performed based on the determined location of interest. The system of claim 1, wherein before generating the first difference image based on the result of separately aligning the first image to the design, the first difference image and the test image portion of the first image are mutually exclusive Align. A system as claimed in claim 1, wherein the sample is a wafer. The system of claim 1, wherein the imaging subsystem is further configured to generate the first image and the second image using light. The system of claim 1, wherein the imaging subsystem is further configured to use electrons to generate the first image and the second image. A non-transitory computer-readable medium storing program instructions that can be executed on a computer system to execute a computer-implemented method for aligning images of a sample generated using different modes of an imaging subsystem, wherein the computer-implemented method includes: generating a first image and a second image of the sample using a first mode and a second mode of the imaging subsystem, respectively; separately aligning the first image and the second image to a design of the sample; for a position of interest in the first image, generating the position of interest by subtracting a first reference image of the position of interest from a test image portion of the first image of the position of interest. A first difference image is placed; a second difference image of the concerned position is generated by subtracting a second reference image of the concerned position from a test image portion of the second image of the concerned position; the first difference image and the second difference image are aligned with each other; and information of the concerned position is determined from a plurality of results of aligning the first difference image and the second difference image with each other, wherein determining the information includes: verifying whether the separate alignment is accurately performed, and wherein the separate alignment, generating the first difference image, generating the second difference image, aligning the first difference image and the second difference image, and determining the information are performed by the computer system. A computer-implemented method for aligning images of a sample generated using different modes of an imaging subsystem, which includes: using a first mode and a second mode of the imaging subsystem to generate a first mode of the sample, respectively. image and a second image; separately aligning the first image and the second image to a design of the sample; for a position of interest in the first image, by taking the third image from the position of interest A first difference image of the location of interest is generated by subtracting a first reference image of the location of interest from a test image portion of an image; by subtracting a test image portion of the second image of the location of interest. removing a second reference image of the location of interest to generate a second difference image of the location of interest; aligning the first difference image and the second difference image with each other; and from the first difference image and The plurality of results of the second difference images aligned with each other determine the information of the position of interest, wherein determining the information includes: verifying whether the separation is accurately performed Alignment, wherein one or more computer systems perform the separate alignment, generate the first difference image, generate the second difference image, align the first difference image and the second difference image and determine the information.